1. Field of the Invention
The present invention generally relates to a rotor unit to which a storage disk is fixed, a motor including the rotor unit, and a storage disk drive including the motor.
2. Description of the Related Art
A storage disk drive such as a hard disk conventionally includes a spindle motor for rotationally driving the storage disk(s) arranged on a rotor hub of the spindle motor (such spindle motors will be simply referred to as a motors hereinafter). One bearing mechanism that has been used in the motor is a fluid dynamic-pressure bearing mechanism (hereinafter simply referred to as FDB), in which the hydrodynamic pressure induced in lubricating oil retained between a stator unit (e.g., a sleeve unit fixed to a base plate of the motor) and a rotor unit (e.g., a shaft fixed to the rotor hub and inserted into the sleeve) is used for rotatably supporting the rotor unit.
Generally, in the manufacture of the motor, the shaft is loosely fitted into a mounting hole arranged in the rotor hub and then is fixed to the rotor hub with an adhesive. Alternatively, the shaft is interference-fitted into the mounting hole. If the adhesive is used for fixing the shaft and the rotor hub, the shaft and the rotor hub need to be retained on a jig until the adhesive hardens. When a portion of the shaft that is interference-fitted to the rotor hub has an axially shorter length, the shaft is not firmly fixed to the rotor hub and the perpendicular orientation of the shaft relative to the rotor hub may be degenerated. By making the portion of the shaft that is interference-fitted to the rotor hub axially longer, excessive load is applied to the shaft, deforming the shaft upon interference-fitting thereof. The deformed shaft may degrade the perpendicularity of the rotor hub, and the lubricating oil used in a bearing mechanism of the motor may leak to the outside of the motor along an outer circumferential surface of the deformed shaft.